Method of making thick sheets of bonded asbestos



A ril 9, 1929. .1. c. M ILDOWlE 1,708,842

METHOD OF MAKING THICK SHEETS OF BONDED ASBESTOS Filed Nov. 15, 1927Patented ihpn 9 ZFUHN U, llIACIlIIBUWXE, (3F NASHUA, HEWHAlllllhHltlEtE, ASEHEGHUR ll'tl ASBESTOS W001i) do SHINLGZLE $0., @IENASHUA, NEW HAMPSHHRE, .l-l. UURlE'ORlldlllflll' Uh bl'lElW HAMP-SHEER-4F,

llI'TlHOD 01 MAKING THIGK'E'HEETS Uh BEBlIZDED AhEEEtTlIlEl.

hpplication filed November 15, 19537. fierial llo. $433,380.

This invention relates to the formation of bloclrs, slabs and the likeof fibre-concrete and has for its object the production of plates orslabs of greater thickness than has heretofore been found practicable toattempt, and relates particularly to the manu'lacturc cl such articlesby filter compression from water suspensions of the solid constituentsof the concrete such for instance as are exeniplified by the product nowcommercially known as asbestos Wood. The relative proportions ot'asbestos libre and hydraulic cement which form the solid constituents oisu h suspension may vary as also the proportion between the solidconstituents taken as a Whole and the water which is the vehicle ofsuspension; as a practical rnatter however there is a limit below whichthe Water percentage may not safely be reduced-tor the reason that asuspension too rich in solids and too thick develops a tendency to termballs or lumps in the suspension which retain their individuality,present diiliculties to the expression of Water, and persist in thefinally consolidated and set slab serious detects in structure.lhere'lore with a filter press cl any given depth capacity there is alimit to the thickness of the slab or sheet producible, imposed by thispractical limit of the ratio between the Water vehicle and the solids.

With the mixtures used in the manufacture oi? asbestos Wood for instaiueratio the employment or a water suspension of the fibre and cementconstituents Of {our parts Water to one of solids is practically certainto yield uniform and satisfactory results.

By this method herein described slabs of such a fibre-concretethoroughly integrated and free from lamination and tar thicker than haveheretofore been produced or producible in a press of any given depthcapacity may be made Without departing from the approved safe andpreferable proportions of Water and solids in the suspension of solidsintroduced into the receiving chamber of the press.

The drawing hereto annexed, which represents diagrammatically the upperand lower 1 1 1 n heads oi a filter press, 'Wlll assist in the enfilterbed Q to be discharged trons suitably arranged channels 5.

Assuming a Water suspension ot' the solid constituents of afibre-concrete in which the ratio of water to solid is l to l; the pressbed illustrated will be first char ed with a mass of such suspensionwhich lills the receiving chamber to the level indicated by the dottedline 5. ldhould the charge thus introduced be subjected to pressure, thewater of sus pension expressed therelronu and the pressure accumulatedto the point required to condense thoroughly and finally the solidconstituents with only such Water remaining associated therewith as willresist expression from the solids by further increase cl pressure, thethickness at the completely con densed rnass "will be substai lly lessvthan that represented 'tEllEl l indicated in the drawing lying betweenthe lilter bed 2 and the line l1. practice this complete condensationpressure approximates lOOll pounds to the square inch. lnstecd ofproceeding to such complete condensation, the

press heads are made to approach, express 3 ing the Water ol suspensionlroin the solids and through the filter bed and by manipulation of thecontrols of the press this pressure is not allowed to exceed a value ofthe order oft 100 pounds to the square inch and when the gages Show thatfurther approach of the press heads to each other Will raise thepressure from such predetermined moderate and safe value the heads areseparated. The massthus produced andlying upon the filter bed 2, whilecondensed into a'slab or cake is nevertheless'solt, yielding to pressureof the fingers. Enough Water remains associated with the solidconstituents to hold them much further apart than would have been thecase it the com lete consolidating or condensing pressure ad beenapplied. This lightly pressed or semi-condensed slab this'ycondition isdemonstrated by the fact.

that if pressure were to be raisedfrom the moderatevalue, at whichincrease of pressure was arrested, water would continue to be expressedfrom the mass, filtering down through until the ultimate pressure wasreached.

Then a second charge of asimilar water suspension of concrete materialsis intro duced into the receiving chamber, filling it this time about tothe level marked 9; the press heads I are made to ap roach and the waterof this suspension isl iltered through the underlying body 8 and theexpression continued until the second charge is compressed to adepth-indicated bythe line 10.

During the compression of this second charge 1 11 the .water ofsuspension passing into. and through the previously semi-condensedcharge 8 carries with it into the interstices of the mass 8 some of thefibre and cement contained in the second charge, so that when thepressure on charge 11 is arrested, say at a value of about 100 pounds tothe square inch and at a time when the increase of pressure sh: ..'s itstendency toward a final rise, the two successively introduced chargeshave become practically integrated, the original upper surface at 7- ofthe lower semi-condensed charge has disappeared, and the body of one hasmerged in the body of the other. If a greater thickness of product isdesired a third charge of a water suspension of fibreconcrete materialsis introduced into the press chamber and'wil'l fill it about to thelevel marked'12. The press is then operated and the water of this thirdsuspension is expressed from it through the underlying filter mass 8,11, and the fibre and cement constituents of the third charge 13 arecarried into the interstices of the portion 11 integrating the materialsof the third charge with those of the second. Assuming now that thedesired thickness of the product has been reached, the pressure on thethree accumulated successive char es 18 made to rise unsure which isabout 4000 pounds to the square inch. ,During this stage the residualwater contained in the material 8-1113 will be squeezed out of itandtherewillremain with the 7 solid constituents the non-expressible waterwhich eventually functions in the final setting of the concrete mass.The reduction in thickness during the application of increasing tofinalpr essure'will not be very great. It has been found advisable'inprac-' ties to hold the final pressure of say 4.000 pounds to the squareinch for a short time after it has been attained, then to release it,Without however retracting one press head from the other, allowin thepressureto fall to say 300 or400 pouni; to the square inch,

and after this release then to accumulate the, pressure again to thehigh limit of about 4000 pounds. Ithas been discovered by experiencethat material which apparently is resisting further condensation at thefirst application of 4000 pound pressure will after such release andreapplication undergo further, though slight, condensation whichconsiderably enhances the density and final strength of the material.When the material has thus been accumulated to the desired thickness'andhas been finally condensed, the press heads are withdrawn from eachother, the block made up of the successive charges 8-1113 clinging tothe smooth imperforate surface of the head 3 from which it can be easilydetached and dropped upon a suitable rack by merely oosening one edge ofthe material from the press head. After being withdrawn from the pressthe material is stacked with other similar-slabs and the concrete isallowed to set. a

It will now be obvious that in a press of any given depth capacity athoroughly homogeneous, non-laminated slab of the character describedmay be made of much greater thickness than would otherwise be possible.

Claims:

1. Method of forming fibre-concrete, characterized by partiallycondensing the solid constituents of a mass of fibre-concrete, by

expression of water from a. water suspension thereof, then condensing amass of similar water suspension by expressing water therefrom throughthe formerly partially con-' densed mass to integrate the two saidmasses, thereafter applyin pressure to the thus united masses to e ectmaximum condensation by expression therefrom of residual water ofsuspension, and allowing the product to set.

2. Method of forming fibre-concrete, characterized by partialcondensation of the solid constituents of masses of fibre-concrete byexpression of water from a water suspension. thereof, in success1vesuperposition, ex-

pressing the water from each suspension through the partially condensedsolids previously thus treated to integrate the solid constituents ofsuccessively pressed masses, applying pressure to thus unitedsuccessively partlally compressed masses to effect maxi mum condensationof the solids by expression therefromvof residual water of suspension,and allowing the product to set.

3; Method Y condensed mass to integrate the two masses, applying anincreased pressure to the thus of forming fibre-concrete, characterizedby partially condensing the solid constituents of a mass offibre-concrete integrated masses, releasing such pressure,

and then applying a, final pressure thereto, to

effect the maxlmum condensation required by of residual water ofacterized by partially condensing the solid constituents of a mass offibre-concrete by expression of water from a water suspension thereofunder pressure, releasing such ressure Without permitting expansion 0the condensed mass, and applying an increased pressure thereto, toeffect the maximum condensation required by expression therefrom ofresidual water of suspenslon.

Signed by me at Nashua, New Hampshire,

this twelfth da of November, 1927 I OHN C. MA ILDOWIE

